In automotive OEM finishing, the interior parts of the automobile bodies are normally first painted by pneumatic spraying or compressed air spraying. Pneumatic spraying is selected because the cavities and recesses are difficult to coat electrostatically, owing to the formation of Faraday cages.
For the painting of the interior, the doors are opened and, by hand or using an automatic painting device, the rabbets and the insides of the doors are painted. This, however, produces a spray mist which falls onto the outside of the body. The area around the doors and the hood are particularly affected by this phenomenon. When powder clearcoat slurries are used, this spray mist dries particularly rapidly and, in the course of subsequent electrostatic coating of the exterior parts of the body, it is only covered by, rather than being taken up again into, the powder clearcoat slurry employed for said exterior coating. At those points where the spray mist landed, therefore, after baking there are elevations or leveling defects which become visible at a size of more than 0.5 μm. Since, moreover, these elevations or leveling defects are present on regions of the body which are particularly easy to see, they are especially evident and give rise to the impression that the product as a whole is of inadequate quality.
These effects are not so pronounced with solventborne clearcoat materials, since these materials have higher solids contents, so that the difference between the solids content of the wet paint and the solids content of the spray mist is lower than in the case of the powder slurry clearcoat materials. Moreover, the solventborne clearcoat materials have a lower viscosity and, consequently, they spread more effectively. As a result, the spray mist too becomes flatter. Not least, because of the presence therein of high-boiling organic solvents (“long solvents”) they do not dry so rapidly and can therefore be taken up much more effectively by clearcoat materials applied over them.
It is an object of the present invention find a novel process for producing multicoat color and/or effect paint systems on automobile bodies which no longer has the disadvantages of the prior art but instead, even when using powder slurry clearcoat materials, gives paint systems which no longer exhibit any visible elevations or leveling defects.